Thermal printers have many applications, one of which is printing one or more lines of the text or other information on a printed medium having a plurality of print areas. In some applications, the same or different information is printed on the different print areas. For example, thermal printers are often employed to print the same expiration date or other information on flexible wrappers and packaging for perishable food items and other articles. For printing purposes, a plurality of these packages or wrappers, each having a designated print area for the printed expiration date or information, may be in the form of a unitary printed medium that is fed to the thermal printer for printing, and later processed for packaging or shipping. Thermal printers may also be used to print information directly on a packaged article or on the article itself. Other applications for print thermal printers include printing information on a semi-rigid printed medium for example, a wallet size plastic card fed to the thermal printer for printing. Print quality requirements also vary from application to application. In the expiration date example given above, for instance, a high resolution text may not be required, and for economical reasons, a legible, low resolution text is often paramount. In other applications, like the wallet size plastic card application, it is desirable to print an aesthetic, high resolution text, graphics, or bar codes. These are only a few examples of the many applications of thermal printers.
Thermal printers generally comprise a thermal print head with an array of heating elements that are movable in relation to a print ribbon having a thermally sensitive ink layer disposed adjacent to a print area of the printed medium. The print ribbon typically comprises a thin ribbon substrate having a layer of thermally sensitive ink disposed on a surface thereof. Printing occurs during a print stroke during which the heating elements of the print head are selectively energized to heat portions of the print ribbon which deposit thermally sensitive ink onto the print area of the printed medium as the print head moves in relation thereto. Heating the print ribbon, however, causes portions of the ink layer to be removed or depleted from the ribbon substrate corresponding to areas that were heated by the print head. Reheating an area of the print ribbon depleted of ink during a previous print stroke does not result in any further deposition of ink onto the printed medium, and therefore ink depletion areas of the print ribbon may not be reused by the print head. In order for the thermal printer to print on another print area of the printed medium in a subsequent print stroke the print ribbon must be moved to position a non-ink depleted area of the ribbon adjacent to the next print area of the printed medium.
In the past, the print ribbon has been positioned to move the ink depletion areas away from a next print area of the printed medium, and to position an inked area of the print ribbon adjacent to the next print area of the printed medium. Re-positioning the print ribbon in this manner however leaves substantial inked portions of the print ribbon unused which results in wasted print ribbon and unnecessary costs. For example, after each print stroke, inked portions of the print ribbon often remain between ink depletion areas corresponding to characters printed during the print stroke. Further, arbitrary re-positioning of the print ribbon after each print stroke to ensure that the print head does not over-lap an ink depletion area during a subsequent print stroke, may result in failure to print with other useful inked areas of the print ribbon. Inefficient use of the thermally sensitive ink on the print ribbon results in increased print ribbon consumption and decreased productivity while replacing a used print ribbon which further increases costs. Print ribbon costs are characterized by the cost of the print ribbon substrate and the cost of the thermally sensitive ink layer disposed on the print ribbon substrate. The cost of the ink is a substantial element of print ribbon cost. More efficient use of the ink on the print ribbon will decrease print ribbon usage, which will result in substantial cost savings.
In view of the discussion above, there exists a demonstrated need for an advancement in the art of a thermal printing.
It is therefore an object of the present invention to provide a novel method and apparatus for thermal printing.
It is also an object of the present invention to provide a novel method and apparatus for a thermal printer that reduces print costs by efficient utilization of a thermally sensitive ink disposed on a print ribbon. Efficient use of the print ribbon results in less print ribbon consumption, and in fewer production interruptions, such as delays for ribbon changes, thereby reducing printing costs.
It is also an object of the present invention to provide a novel method and apparatus for a thermal printer that uses a print ribbon with an series of detectable indices spaced along a surface thereof.
It is another object of the present invention to provide a novel method and apparatus for a thermal printer that uses software and/or mechanical means to control displacement of the indexed or non-indexed print ribbon an incremental interval after one or more print strokes based on the number of indices detected or based on recorded movement of the ribbon. In one embodiment, the print ribbon is displaced an incremental interval that permits the print head to utilize adjacent areas of the print ribbon during subsequent print strokes with some over-lap of the ink depletion areas of the print ribbon. In an alternative embodiment, the displacement of the print ribbon is increased to prevent the print head from over-lapping ink depletion areas during a subsequent print stroke to improve print quality.
It is another object of the present invention to provide a novel method and apparatus for a thermal printer that uses software to control displacement of the indexed print ribbon based on a number of print strokes that occur during the detection of two adjacent indices. The number of print strokes counted between two adjacent indices may be compared to a reference number, for example the number of print strokes counted between two previous indices.
It is further object of the present invention to provide a novel method and apparatus for a thermal printer having a software controlled print head that generates different character fonts that decrease usage of the ink on the indexed print ribbon and therefore permit more characters to be printed with the indexed print ribbon. In one embodiment, the print head generates an italic character font. In another embodiment, the print head generates a gray shade font. In both embodiments the print head may over-lap portions of the print ribbon with ink depletion areas formed during a subsequent print stroke without adversely effecting print quality.
It is a further object of the present invention to provide a novel method and apparatus for a thermal printer having a software controlled print head that laterally shifts characters during a subsequent print stroke to utilize ink on a portion of the print ribbon between ink depletion areas formed during a previous print stroke.
It is yet a further object of the present invention to provide a novel method and apparatus for a thermal printer having a software controlled print head that selects an appropriate character font and laterally shifts characters during a subsequent print stroke, and a software controlled means for displacing an indexed print ribbon an incremental interval after a print stroke to reduce print costs. Laterally shifting printed characters distributes the work load of the print head which increases the life expectancy of the print head.
It is still a further object of the present invention to provide a novel method and apparatus for a thermal printer that optimizes print ribbon ink usage only upon the occurrence of some event, for example, the actuation of a switch.
It is a also an object of the present invention to provide a novel method and apparatus for a thermal printer that uses only a print ribbon on a supply and take-up reel having a core that enables the optimization of print ribbon ink usage.
Accordingly, the present invention is directed toward a novel method and apparatus for low cost thermal printing in a thermal printer having a software controlled thermal print head that moves in relation to an indexed print ribbon with a thermally sensitive ink layer disposed adjacent to a printed medium, such as a package for a product. The thermal print head comprises a linear array of heating elements that are selectively energized to heat the print ribbon which deposits ink onto the printed medium as the print head moves in relation to the print ribbon in a print stroke. In two specific embodiments, the heating elements may be either resistive or light-emitting elements. The cost of printing may be decreased by efficient use of the ink on the print ribbon. Between print strokes or after the completion of a number of print strokes, the print ribbon is displaced an incremental interval to position an unused portion of the print ribbon adjacent to a next print area of the printed medium. The displacement of the print ribbon is also software controlled. The amount of specific displacement may be controlled by the ribbon feeding means, without the use of indices on the ribbon, or may be based on the detection of discontinuities or indices disposed at intervals along the print ribbon. In one embodiment, the indices are a series of relatively reflective areas or glossy stripes formed along a matte surface of the ink layer, which are detected by sensing a light reflected from the print ribbon. The relatively matte areas may contain the same, more, or less ink than adjacent areas. The utilization of ink on the print ribbon is also made more efficient by selecting or generating an appropriate character font with the print head. In one embodiment, the print head generates a slanted character font which creates an ink depletion area on the print ribbon that may be closely stacked or nestled next to an ink depletion area caused by a subsequent print stroke. Certain italic character fonts are also comprised of thin lines that tend to obscure small areas where no ink is deposited due to the print head over-lapping ink depletion areas of the print ribbon during a subsequent print stroke. In an alternative embodiment, the print head generates a gray shade character font or a font formed of a plurality of parallel lines. The thin lined, slanted line, and shaded fonts require less ink than do some other types of fonts and therefore use less ink on the print ribbon during the print stroke. Also, use of these fonts reduces the degradation of visual image quality which may otherwise result from the ink saving measures. By reducing the areas of ink depletion on the print ribbon, the print ribbon displacement interval between print strokes may be decreased, and some portions of the print ribbon may be over-lapped by the print head during a subsequent print stroke thereby reducing print costs without adversely effecting print quality. The utilization of ink on the print ribbon may also be made more efficient by laterally shifting the printed characters during subsequent print strokes in addition to selecting an appropriate character font and controlling the incremental displacement interval of the print ribbon as discussed above. Lateral shifting of characters during subsequent print strokes permits the utilization of ink between areas on the print ribbon where ink was depleted in a previous print stroke. Lateral shifting of characters also permits the print ribbon displacement interval to be decreased and further permits some portions of the print ribbon to be over-lapped by the print head during subsequent print strokes without adversely effecting print quality. Lateral character shifting and generation of the character fonts is accomplished by selectively energizing the heating elements of the print head during the print stroke, and these functions are readily controlled by software, for the purpose of reducing print costs. However, the shifting may also be accomplished by mechanical means. In another embodiment, the thermal printer optimizes print ribbon ink usage as discussed above only upon the occurrence of some event, for example, the actuation of a switch, or in an alternative embodiment, by using a print ribbon on a supply and take-up reel having a core that enables the optimization of print ribbon ink usage.
These and other objects, features and advantages of the present invention will become apparent upon consideration of the following Detailed Description of the Invention with the accompanying drawings.